Header conversion technique

ABSTRACT

A header conversion device allowing reduced amount of hardware and memory and high-speed line switching is disclosed. In an ATM switching device having redundant incoming line systems, a header conversion table stores a set of header conversion information for one of the redundant incoming line systems. A header converter converts the header of an ATM cell received from each of the redundant incoming line systems by referring the same set of header conversion information.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to an ATM (asynchronous transfer mode) switching device capable of switching one of lines to another of the lines, and in particular to a header conversion technique for the line switching.

2. Description of the Related Art

In general, an ATM switching device having line protection capability is provided with a header converter and a header conversion table, which are used to switch a working line to a reserved line. More specifically, a plurality of line interfaces are connected to a multiplexer, which multiplexes incoming rixed-length packets (cells) received from the respective line interfaces to produce a sequence of cells each having the incoming line number thereof attached therewith. When receiving the sequence of cells from the multiplexer, the header converter reads the incoming line number and VPI/VCI (Virtual Path Identifier/Virtual Channel Identifier) for each cell and uses them as a key to search the header conversion table for output information necessary for a switch fabric to forward the cell to an appropriate output port thereof. The header converter converts the header of the cell using the found output information. Such output information includes an outgoing line number outgoing routing information VPI/VCI, and control information for controlling the quality of service for each cell flow. The header conversion technique as described above has been disclosed in Japanese Patent Application Unexamined Publication Nos. 7-74747 and 10-79747.

In the case of redundant system architecture, however, two memory areas used for respective ones of working system and reserved system are needed to store the same information in the header conversion table, resulting in the increased amount of hardware and the increased amount of memory for header conversion table.

As shown in FIG. 1, for example, a 1+1 redundant system having #0 (working) and #1 (reserved) incoming lines includes a header conversion table storing necessary information for respective ones of #0 and #1 incoming lines. When the working line normally functions, the header converter accesses a set of information for the #0 incoming line to obtain necessary information for the switch fabric to forward the cell to an appropriate output port thereof. If the working line is switched to the reserved line due to occurrence of a failure on the #0 system, then a set of information to be accessed is changed from the #0 incoming line to the #1 incoming line.

Therefore, if the set of information for the #0 incoming line is not identical to that for the #1 incoming line, then the line switching cannot be successfully performed. It is necessary to always store the same set of information for the #0 and #1 incoming lines in the header conversion table.

It is the same with the case of N:1 redundant system having N working incoming lines and a single reserved incoming line. In this case, it is further necessary to copy the latest information after a failure has occurred on the working incoming line to a memory area for the reserved incoming line. Since the table duplication is needed after the occurrence of a failure, it is not possible to perform the line switching immediately after the failure occurs and therefore the increased speed of line switching cannot be achieved.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a header conversion method and device eliminating the need of information for a reserved system, allowing reduced amount of hardware and memory.

Another object of the present invention is to provide a header conversion method and device allowing high-speed line switching when a failure occurs.

According to the present invention, a device for converting a header of a packet to forward the packet to an appropriate one of output ports of a switch fabric, includes: redundant incoming line systems: a header conversion table storing a set of header conversion information for one of the redundant incoming line systems; and a header converter for converting a header of a packet received from each of the redundant incoming line systems by referring the set of header conversion information.

According to an aspect of the present invention, a device for converting a header of a packet to forward the packet to an appropriate one of output ports of a switch fabric, includes: at least one line interface; a reserved line interface corresponding to each of said at least one line interface; a selector for normally selecting a corresponding line interface to receive a packet stream and, when a failure occurs on a system corresponding to the corresponding line interface, selecting the reserved line interface to receive the packet stream: a header conversion table storing header conversion information for each of said at least one line interface; and a header converter for converting the header of a packet received from the reserved line interface selected by the selector by referring to the header conversion information for the corresponding line interface.

The at least one line interface and the reserved line interface have line numbers uniquely assigned thereto. A line number of each of said at least one line interface and the reserved line interface may be transferred to the header converter. The header converter may include: a line number converter for converting a line number of the reserved line interface to a line number of the corresponding line interface; and a controller for accessing the header conversion information for the corresponding line interface by using the line number of the corresponding line interface. When the reserved line interface is selected by the selector due to occurrence of the failure, the line number converter may convert the line number of the reserved line interface to the line number of the corresponding line interface.

According to another aspect of the present invention, a device for converting a header of a packet to forward the packet to an appropriate one of output ports of a switch fabric, includes: a plurality of line interfaces connected to respective ones of incoming lines; a reserved line interface; a first selector for connecting a selected one of the incoming lines to the reserved line interface when a failure occurs on a system corresponding to a corresponding line interface: a second selector for normally selecting each of the plurality of line interfaces and when the failure occurs on the system corresponding to the corresponding line interface, selecting the reserved line interface in place of the corresponding line interface; a header conversion table storing header conversion information for each of the plurality of line interfaces; and a header converter for converting the header of a packet received from the reserved line interface selected by the second selector by referring to the header conversion information for the corresponding line interface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing a conventional header conversion method;

FIG. 2 is a block diagram showing an input stage of an ATM switching device employing a header conversion method according to a first embodiment of the present invention;

FIG. 3 is a block diagram showing the input stage of the ATM switching device of FIG. 2 for explanation of an operation of the first embodiment;

FIG. 4 is a schematic diagram showing a header conversion method according to the first embodiment;

FIG. 5 is a block diagram showing an input stage of an ATM switching device employing a header conversion method according to a second embodiment of the present invention:

FIG. 6 is a block diagram showing the input stage of the ATM switching device of FIG. 5 for explanation of an operation of the second embodiment;

FIG. 7 is a schematic diagram showing a header conversion method according to the second embodiment;

FIG. 8 is a block diagram showing an input stage of an ATM switching device employing a header conversion method according to a third embodiment of the present invention;

FIG. 9 is a block diagram showing the input stage of the ATM switching device of FIG. 8 for explanation of an operation of the third embodiment; and

FIG. 10 is a schematic diagram showing a header conversion method according to the third embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 2, an ATM switching device employing a header conversion circuit according to a first embodiment of the present invention is provided with a line interface section 1 accommodating N incoming lines.

The line interface section 1 includes N (N is an integer greater than 1) line interfaces 11.1 to 11.N, each of which is connected to a corresponding incoming line to receive data from another ATM switching device or a subscriber communication device.

Further, the respective line interfaces 11.1 to 11.N have line numbers (here, #0 to #N−1) uniquely assigned thereto. A cell output of each of the line interfaces 11.1 to 11.N is connected to a multiplexer 2 and a sequence of cells multiplexed by the multiplexer 2 is output to a header conversion section 3. The header conversion section 3 includes a header converter 31, a line number converter 32, and a header conversion table 33.

The header converter 31 outputs the line number and the routing information VPI/VCI for each cell to the line number converter 32 and the header conversion table 33, respectively. The header converter 31 receives necessary information corresponding to the line number and the routing information from the header conversion table 33 and converts the header of each cell using the necessary information. The cell with converted header information is transferred to the switch fabric (not shown), in which the cell is forwarded to an appropriate output port of the switch fabric depending on the converted header information.

As shown in FIG. 3, the multiplexer 2 multiplexes incoming fixed-length packets (cells) received from the respective line interfaces 11.1 to 11.N according to a multiplexing control signal to produce a sequence of cells. The sequence of cells is output to the header converter 31 with each cell having the line number of a corresponding line interface at which the cell arrived.

When receiving the sequence of cells from the multiplexer 2, the header converter 31 reads the line number and routing information VPI/VCI for each cell and outputs the line number to the line number converter 32 and the routing information VPI/VCI to the header conversion table 33. A converted line number by the line number converter 32 is output to the header conversion table 33.

In the case of a redundant system, the line number converter 32 allows the line number to be converted to selected line number depending on a control signal. Since the system as shown in FIG. 2 has no redundant architecture, the line number converter 32 does not substantially convert the line number.

Referring to FIG. 4, the line number and the routing information VPI/VCI for each cell are used as a key to search the header conversion table 33. For example, when receiving a cell arriving at the line interface 11.1 having line number #0 assigned thereto, since the line number is not converted by the line number converter 32, the line number #0 and the routing information VPI/VCI of the cell are used as a key to search the header conversion table 33. When a match is found, the corresponding output information composed of an outgoing line number, outgoing routing information VPI/VCI, and control information is returned to the header converter 31. Using the output information returned from the header conversion table 33, the header converter 31 converts the header of the cell and outputs the cell with converted header to the switch fabric.

In general, the header conversion table 33 includes a decoder or CAM (Contents Addressable Memory) and a random access memory (RAM) storing output information. After the line number and the routing information VPI/VCI are converted to a memory address by the decoder or CAM, the output information stored in the RAM is accessed according to the memory address and is returned to the header converter 31.

1+1 Redundant System

Referring to FIG. 5, an ATM switching device employing a header conversion circuit according to a second embodiment of the present invention has a 1+1 redundant architecture, in which circuit blocks similar to those previously described with reference to FIG. 2 are denoted by the same reference numerals.

A line interface section 4 accommodates a working line 401 and a reserved line 402, which are connected to a line interface 41.1 and a line interface 41.2, respectively. Here, line numbers #0 and #1 are assigned to the line interface 41.1 and the line interface 41.2, respectively. Plural line interface sections having the same circuit as the line interface section 4 may be connected to the multiplexer 2.

When normally operating, the same data is transferred on both the working line 401 and the reserved line 402. However, the multiplexer 2 multiplexes cells received from only working line interfaces to produce a sequence of cells according to a multiplex control signal. In such a normal condition, the operation of the header conversion section 3 is the same as that in the first embodiment as shown in FIG. 4.

As shown in FIG. 6, in the event of a failure on the working line 401 or the line interface 41.1, the occurrence of the failure is detected by a well-known means and thereby the multiplex control signal is changed so as to control the multiplexer 2 such that cells received from the line interface 41.2 connected to the reserved line 402 are selected to be multiplexed. At the same time, the conversion control signal causes the line number converter 32 to switch the line number #1 to the line number #0.

Referring to FIG. 7, more specifically, when the multiplexer 2 switches an incoming route from the line interface 41.1 to the line interface 41.2 in response to the occurrence of the failure, cells output from the line interface 41.2 having the line number #1 assigned thereto are multiplexed and transferred to the header converter 31 together with the line number #1.

The header converter 31 reads the line number #1 and the routing information from each of the cells and outputs them to the line number converter 32 and the header conversion table 33. Since the line number converter 32 has been set to such a state that the working line number #1 is converted to the reserved line number #0, the output information corresponding to input information for the line number #0 is accessed and returned to the header converter 31. In other words, the header converter 31 can obtain the same output information as in the normal case from the header conversion table 33 after and before the failure on the working line 401 occurs. Accordingly, the cells on the reserved system can be transferred to the switch fabric as the case of the cells on the working system without the need of the installation of information for the reserved system in the header conversion table 33.

N:1 Redundant System

Referring to FIG. 8, an ATM switching device employing a hoader conversion circuit according to a third embodiment of the present invention has an N:1 redundant architecture, in which circuit blocks similar to those previously described with reference to FIG. 2 are denoted by the same reference numerals.

A line interface section 5 includes a working line interface section 5 a composed of N working line interfaces 51.1 to 51.N corresponding to respective ones of N working lines 401, 402, 403, —and a reserved line interface 51. (N+1). Here, line numbers #0 to #N are assigned to the working line interfaces 51.1 to 51.N and the reserved line interface 51. (N+1), respectively.

In addition, a selector switch 6 is connected between the N working lines and the reserved line interface 51. (N+1). The selector switch 6 has N input ports connected to respective ones of the N working lines and one output port connected to the reserved line interface 51. (N+1). When one of the working line interfaces 51.1 to 51.N is faulty, the selector switch 6 is switched by a selection signal so that the reserved line interface 51. (N+1) is used in place of the fault line interface. The working and reserved line interfaces 51.1 to 51. (N+1) are connected to the multiplexer 2.

When normally operating, the multiplexer 2 multiplexes cells received from only working line interfaces 51.1 to 51.N to produce a sequence of cells according to a multiplex control signal. In such a normal condition, the operation of the header conversion section 3 is the same as that in the first embodiment as shown in FIG. 4.

As shown in FIG. 9, in the event of a failure on the working line interface 51.1, the occurrence of the failure is detected by a well-known means because no cell is received from the working line interface 51.1. When the occurrence of the failure is detected on the working line interface 51.1, the selection signal is changed so as to connect the working line 401 corresponding to the fault line interface 51.1 to the reserved line interface 51. (N+1) and thereby incoming cells on the working line 401 are transferred to the reserved line interface 51. (N+1). Further the multiplex control signal is changed so as to control the multiplexer 2 such that cells received from the reserved line interface 51. (N+1) are selected to be multiplexed. At the same time, the conversion control signal causes the line number converter 32 to convert the line number #N to the line number #0.

Referring to FIG. 10, more specifically, when the multiplexer 2 switches an incoming route from the line interface 51.1 to the reserved line interface 51. (N+1) in response to the occurrence of the failure, cells output from the reserved line interface 51. (N+1) having the line number #N assigned thereto 1.0 are multiplexed and transferred to the header converter 31 together with the line number #N.

The header converter 31 reads the line number #N and the routing information from each of the cells and outputs them to the line number converter 32 and the header conversion table 33. Since the line number converter 32 has been set to such a state that the line number #N is converted to the line number #0, the output information corresponding to input information for the line number #0 is accessed and returned to the header converter 31. In other words, the header converter 31 can obtain the same output information as in the normal case from the header conversion table 33 after and before the failure on the working line interface 51.1 occurs. Accordingly, the cells coming in on the working line 401 can be transferred to the switch fabric through the reserved line interface 51. (N+1) as the case of the cells on the working line interface 51.1 without the need of the installation of information for the reserved line interface 51. (N+1) in the header conversion table 33.

In the above embodiments, the line number converter 32 is provided in the header conversion section 3. Alternatively, it is possible to provide the line number converter 32 in the reserved line interface 41.2 or 51. (N+1) or the multiplexer 2. Further, it is possible to provide the line number converter 32 on the cell transfer line between the multiplexer 2 and the header conversion section 3.

As described above, there is no need of a conversion table used for a reserved line interface, resulting in the reduced size of a decoder or CAM for converting the routing information to a memory address and further the reduced amount of memory required for the header conversion table. This may promote miniaturization and achieve cost-reduction effectively.

Since the same table as the working header conversion table is accessed even if switching to the reserved line interface, the identical information can be obtained to convert the header information in both working and reserved systems. Accordingly, it can be avoided that the line switching cannot be successfully performed. Further, in the case of N:1 redundant system, there is no need of the installation of data duplicating means. Since data duplication is not needed, high-speed line switching can be achieved. 

1-17. (canceled)
 18. A device comprising: a first converter to: convert first information, associated with a first interface, to second information associated with a second interface, the second information being different than the first information; and a second converter to: obtain output information corresponding to the second information for a packet associated with the first interface, the output information corresponding to the second information being obtained based on the first information being converted to the second information, and convert, using the obtained output information, a header of the packet.
 19. The device of claim 18, where the first converter is to convert the first information to the second information based on a failure of the second interface.
 20. The device of claim 18, where the second converter is further to transmit a request for output information corresponding to the first information for the packet associated with the first interface, the request including the first information, and where the output information corresponding to the second information is obtained based on the request.
 21. The device of claim 18, where the first interface is associated with a reserved line, and where the second interface is associated with a working line.
 22. The device of claim 18, further comprising a memory to store: first header conversion information associated with the first interface; and second header conversion information associated with the second interface, the second header conversion information including the output information corresponding to the second information.
 23. The device of claim 18, where the first converter is further to: convert the first information to third information associated with a third interface, the third information being different than the first information, and where the second converter is further to: obtain output information corresponding to the third information for another packet that is associated with the first interface, the output information corresponding to the third information being obtained based on the first information being converted to the third information, and convert, using the obtained output information corresponding to the third information, a header of the other packet.
 24. A system comprising: a device to: store output information corresponding to a first interface; convert a header of a first packet using the output information when no failure of the first interface is detected, the first packet being associated with the first interface; convert a header of a second packet using the output information when a failure of the first interface is detected, the second packet being associated with a second interface, the second interface being different than the first interface; and transmit at least one of: the first packet after converting the header of the first packet, or the second packet after converting the header of the second packet.
 25. The system of claim 24, where the device is further to: detect that the first interface is experiencing the failure.
 26. The system of claim 24, where the device is further to: store output information corresponding to a third interface that is different than the first interface and the second interface; obtain, based on a failure of the third interface, the output information corresponding to the third interface for a third packet that is associated with the second interface; and convert, using the obtained output information corresponding to the third interface, a header of the third packet.
 27. The system of claim 26, where the device is further to: convert first information, associated with the second interface, to second information associated with the third interface based on the failure of the third interface; and obtain the output information corresponding to the third interface based on the first information being converted to the second information.
 28. The system of claim 24, where the device is further to: obtain the output information corresponding to the first interface for the second packet based on the failure of the first interface.
 29. The system of claim 28, where the device is further to: convert information identifying the second interface to information identifying the first interface based on the failure of the first interface; and obtain the output information corresponding to the first interface based on the information identifying the second interface being converted to the information identifying the first interface.
 30. A method comprising: detecting, by a device, a failure of a first interface; obtaining, by the device, output information for a packet associated with a second interface, the second interface being different than the first interface, the output information corresponding to the first interface, the output information being obtained based on detecting the failure of the first interface; and converting, by the device, a header of the packet using the obtained output information based on detecting the failure of the first interface.
 31. The method of claim 30, further comprising: transmitting the packet after converting the header of the packet.
 32. The method of claim 30, where the first interface corresponds to a working interface, and where the second interface corresponds to a reserved interface.
 33. The method of claim 30, further comprising: storing output information corresponding to a third interface that is different than the first interface and the second interface; obtaining, based on a failure of the third interface, the stored output information corresponding to the third interface for another packet that is associated with the third interface; and converting, using the obtained output information corresponding to the third interface, a header of the other packet.
 34. The method of claim 33, further comprising: converting, based on the failure of the third interface, first information, associated with the second interface, to second information that is associated with the third interface; and obtaining the output information corresponding to the third interface based on the first information being converted to the second information.
 35. The method of claim 34, further comprising: detecting the failure of the third interface; and converting the first information to the second information based on detecting the failure of the third interface.
 36. The method of claim 33, where the third interface corresponds to a working interface, and where the second interface corresponds to a reserved interface.
 37. The method of claim 30, further comprising: converting first information identifying the second interface to second information identifying the first interface based on detecting the failure of the first interface; and obtaining the output information corresponding to the first interface based on the first information being converted to the second information. 